#define _CRT_SECURE_NO_WARNINGS 1
#include<stdio.h>
int main()
{
	int a = 1;
	int b = 2;
	double c = 0;
	int d;
	for (int i = 0; i < 20; i++)
	{
		c += (double)b / a;
		d = b;
		b = a + b;
		a = d;
	}
	printf("%lf", c);
	return 0;

}